Sodium sulphate effect on the mineralogy of ternary blended cements elaborated with activated paper sludge and fly ash

The reaction mechanisms of sulphate ion with the paste was carried out through a microstructure study, which included the use of scanning electron microscopy (SEM), porosity and pore-size distribution and X-ray diffraction (XRD). The results showed that ternary Portland cement was stable against sodium sulphate attack at the conditions here studied. The enhancement of flexural strength was a result of the formation of non-expansive ettringite inside the pores and an alkaline activation of the pozzolanic reaction of additions promoted by the ingress of sulphate and secondary related reactions. Accordingly, the microstructure was strongly refined.